Exposure device for manufacturing a display screen of a colour television picture tube, comprising a rotating lens

ABSTRACT

An exposure device for display screens having either a rotationally symmetric lens, a plane parallel plate or a prismatic plate that rotates during the exposure operation of the device to provide exposed dots on the screen that are of smaller dimensions than the apertures in the mask employed.

United States Patent 91 [111 3,810,196 Batten May 7, 1974 EXPOSURE DEVICE FOR MANUFACTURING A DISPLAY SCREEN OF A COLOUR TELEVISION PICTURE TUBE, COMPRISING A ROTATING LENS Inventor? Piet Gerard Joseph Barten,

Emmasingel, Eindhoven, Netherlands Assignee: U .S. Philips Corporation, New

. York, NY.

Filed: Apr. 25, 1972 Appl. No.: 247,280

Foreign Application Priority Data May 14, 1971 Netherlands 7106619 us. (:1 95/1 R, 313/92 B 1m. 01. G03b 27/00 Field of Search 95/1; 313/92 B [56] References Cited UNITED STATES PATENTS 3,736,848 6/1973 Tsunesa 95/1 R 3,738,234 6/1973 Barten et al. 95/] R 3,282,691 11/1966 Morrell et a1. 313/92 B 3,003,874 10/1961 Kaplan 95/1 R Primary Examiner--Richard M. Sheen Attorney, Agent, or Firm-Frank R. Trifari [57] ABSTRACT An exposure device for display screens having either a rotationally symmetric lens, a plane parallel plate or a prismatic plate that rotates during the exposure operation of the device to provide exposed dots on the screen that are of smaller dimensions than the aper tures in the mask employed.

4 Claims, 3 Drawing Figures Will/9i? PATENTED MAY 7 I974 SHEET 2 0F 2 FIG?) The invention relates to an exposure device for manufacturing a display screen of a colour television picture tube, which device comprises a light source for the optical projection of a pattern of holes in a colour selection mask on a window having a photosensitive layer provided thereon for the manufacture of the display screen.

In a known type of colour television display tube, the display screen consists of a large number of phosphor dots which are arranged in groups of three phosphor dots. Each group consists of a phosphor dot luminescing red under the influence of an electron beam, as well as a phosphor dot luminescing green and blue. A black nonreflecting layer may be present between the phosphor dots, which layer absorbs ambient light and thus contributes to a picture which is rich in contrast. The patterns of phosphor dots are provided, colour by colour, by means of a photosensitive layer which is to be provided during the manufacture of the tube and which is exposed in an exposure device and is then developed. Such a photochemical method is generally known. The black nonreflecting layer is generally provided previously, also by means of a photosensitive layer which is exposed by three successive exposures in the places where the red, the green and the blue phosphor dots are to be provided afterwards. The result of the applied method is a black layer having apertures in the places where the phosphor dots are to be provided.

Since during operation of the colour television display tube three electron beams are produced which transmit the red, the green and the blue picture information, respectively, and which may therefore impinge only upon phosphor dots which luminesce in the colour corresponding to said signal information, a colour selection mask is sued in the tube. The colour selection mask comprises a large number of apertures corresponding to the number of groups of three phosphor 'dots. The three electron beams are converged on the display screen and pass the colour selection mask with a given colour selection angle relative to each other. The colour selection angle and the distance of the colour selection mask to the display screen are such that the electron beams form spots on the display screen which in principle do not overlap each other.

The phosphor dots are present in the places where the electron beams impinge on the display screen. In order to ensure that said places correspond indeed with the phosphor dots and with the apertures in the black nonreflecting layer, the exposure of the photosensitive layer during the above-mentioned photochemical method occurs by means ofa light source and the same colour selection mask which is present in the completed tube. The pattern of holes in the colour selection mask is optically projected on the photosensitive layer. Since the colour selection mask is at the same distance relative to the photosensitive layer as in the completed tube relative to the display screen, an optimum coincidence of the spots of the electron beams and the phosphor dots, respectively the aperture in the black nonreflecting layer is obtained. Since, however, said coincidence can be realized only with a certain tolerance, a certain overlap must exist between phosphor dots and electron spots, that is to say, either the spot must be I larger than the phosphor dot in such manner that the spot always fully overlaps the phosphor dot, or the spot must be smaller than the phosphor dot in such manner that the spot is always present within the phosphor dot.

It is obvious that the already mentioned black nonreflecting layer is more effective in the case of small phosphor dots than in the case of large phosphor dots, because the contrast is increased when the nonreflecting layer has a comparatively large area relative to the area of the phosphor dots. Tubes constructed with such a layer are therefore preferably provided with phosphor dots which are smaller than the spots of the electron beams. The size of the spots of the electron beams is determined by the size of the holes in the colour selection mask. The size of the phosphor dots and the apertures in the black nonreflecting layer, however, is also determined during the above-mentioned photochemical method by the size of the holes in the colour selection mask and, without special measures, will hence be approximately equal to or slightly larger than the size of the spots of the electron beams.

It is an object of the invention to provide an exposure device with which the light distribution behind the holes in the colour selection mask can be controlled. Another object of the invention is to provide an exposure device with which phosphor dots and apertures in the black nonreflecting layer, respectively, can be obtained which are smaller than the holes in the colour selection mask, without said holes being temporarily reduced during the exposure or being enlarged after the exposure by, for example, re-etching which requires an expensive and difficult method.

According to the invention, an exposure device of the type mentioned in the preamble comprises optical means which cause a virtual displacement of the light source, which virtual displacement has'at least a component which is parallel to a tangent plane at the center of the window and the exposure device furthermore comprises means for rotating said optical means about an axis of rotation which extends at right angles to the said plane. By rotating the optical means during the exposure, in combination with the said virtual displacement an annular light source is effectively obtained. As a result of this, light distributions are obtained behind the holes of the colour selection mask which, as a function of the place along a diameter of the phosphor dot to be formed and aperture in the black nonreflecting layer, respectively, have a narrow top. By suitable choice of the properties of the photosensitive layer and the exposure time used, said narrow top may be used to obtain phosphor dots and apertures in the black nonreflecting layer, respectively, which are considerably smaller than the holes in the colour selection mask.

It is to be noted that the use of such penumbra effects is indicated in the Journal of the Society of Motion Picture and Television Engineers" vol. 65. nr. 8, Aug. 1956, pp. 407-410, in which article it is also stated that annular light sources are inter alia favourable for said purpose. The construction of an annular light source of a sufficient intensity, however is not described.

An exposure device according to the invention may be constructed so that the said optical means consist of a rotationally symmetric lens the axis of rotational symmetry of which is parallel to and does not coincide with the said axis of rotation. A rotationally symmetric lens in combination with a light source which is not placed on the optical axis of said lens actually provides the desirable virtual displacement of the light source and, in connection with the rotational symmetry, is easy to manufacture.

An exposure device according to the invention may also be constructed so that the said optical means consists of a lens the thickness of which in one direction at right angles to the said axis of rotation is constant. In its simplest form, such a lens is a prism and provides a virtual displacement of the light source at right angles to the direction in which the thickness of the lens is constant.

A simple embodiment of an exposure device according to the invention is such that the said optical means consists of a plane parallel plate, of which'plane parallel plate the normal on the surface encloses an acute angle with the axis of rotation. As is known, a plane parallel plate causes a parallel displacement of the emanating light ray relative to a light ray incident at an acute angle and hence a useful virtual displacement of 20 the light source.

The invention will be described with reference to the accompanying drawings, which show exposure devices according to the invention.

FIG. 1 describes an exposure device incorporating applicants invention.

FIG. 2 describes a part of the exposure device shown in FIG. 1 describing another modification ofapplicants invention.

FIG. 3 shows a further modification of applicants invention.

The exposure device comprises a housing 1 onwhich a window 2 is provided of a colour television display tube to be manufactured. A photosensitive layer 3 on the window 2 is exposed through holes 4 of a colour selection mask 5. Connection means for the window 2 and the colour selection mask 5 are now shown.

By exposure is performed by means of a light source 6 comprising a gas'discharge tube 7 and a quartz cone 8. Light of the gas discharge tube 7 is concentrated by the quartz cone 8 in the tip 9 of said quartz cone. The tip 9 forms a quasi-punctiform light source. A correction lens 10 ensures that the apparent place of the light source is brought in sufficient agreement with the deflection point of the electron beams in the completed colour television display tube. According to the invention, a lens 11 is used which is mounted in a wormwheel 12 which is rotated by means of a worm 13. The variation in thickness of the lens 11 is the same in all planes parallel to the plane of the drawing. Not counting a slight bend of the lens surface 14, the lens 11 is substantially a prism and produces a virtual lateral displacement of the light beam 15 from the tip 9 of the light source. Thislateral displacement lies in the plane of the drawing in the position shown of the lens 11. By rotation of the lens 11, the virtual light beam portion 15 moves on a circle about the axis of rotation which coincides with the path of the light beam; 15 of the lens and an annular light source is effectively obtained.

FIG. 2 shows an exposure device having rotationally symmetric optical means 11'.

FIG; 3 shows an exposure device having modified optical means comprising an oblique parallel plane plate 11 Of course the invention is not restricted to an exposure device for manufacturing a colour television display tube having red, green and blue phosphor dots separated by a black nonreflecting layer. Colour television display tubes having different numbers and different primary colours may also be manufactured with it, whether or not provided with a black nonreflecting layer. Moreover, the invention is not restricted to an exposure device having a gas discharge tube and a quartz cone. In principle, any light source may be used which, viewed from a point of the colour selection mask, effectively has a part emitting a substantially punctiform light.

What is claimed is:

l. A device for exposing a surface portion of a photosensitive layer to light passing through an aperture in a mask to produce an exposed surface portion smaller in area than the area of the aperture in the mask comprising a light source for emitting a light beam on a first axial path, optical means having an axis of rotation substantially coincident with said first axial path positioned between said light source and the mask in said first axial path for causing a virtual displacement of the light beam and for directing the emerging virtual light beam portion into a second axial path which is substantially parallel to said first axial path, and means for rotating said optical means about said axis of rotation whereby the virtual light beam portion circulating about said first axial path exposes through the aperture in the mask a surface portion of a photosensitive layer which is smaller than the area of the aperture in the mask.

2. A device according to claim 1 wherein said optical means is a plane parallel plate.

3. A device according to claim 1 wherein said optical means is a prismatic plate having a bottom surface or thogonal to said axis and a top surface inclined to said axis at an acute angle.

4. A device according to claim 1 further including additional optical means for adjusting the direction of said second axial path of said virtual light beam portion. 

1. A device for exposing a surface portion of a photosensitive layer to light passing through an aperture in a mask to produce an exposed surface portion smaller in area than the area of the aperture in the mask comprising a light source for emitting a lIght beam on a first axial path, optical means having an axis of rotation substantially coincident with said first axial path positioned between said light source and the mask in said first axial path for causing a virtual displacement of the light beam and for directing the emerging virtual light beam portion into a second axial path which is substantially parallel to said first axial path, and means for rotating said optical means about said axis of rotation whereby the virtual light beam portion circulating about said first axial path exposes through the aperture in the mask a surface portion of a photosensitive layer which is smaller than the area of the aperture in the mask.
 2. A device according to claim 1 wherein said optical means is a plane parallel plate.
 3. A device according to claim 1 wherein said optical means is a prismatic plate having a bottom surface orthogonal to said axis and a top surface inclined to said axis at an acute angle.
 4. A device according to claim 1 further including additional optical means for adjusting the direction of said second axial path of said virtual light beam portion. 